Turbojet engines mounted beneath aircraft wings are typically suspended from a strut by a suspension means adjacent the front and rear of the engine. The suspension means comprises members to support the weight of the engine and to resist the rotational torque generated by the engine. Such suspension means typically comprise support bars or rods having one end fixed to the suspension means and the other to the engine. The rear suspension of the turbojet engine typically comprises three such bars or rods attached by hinge means to an engine casing ring and to three points on a rear strut of the aircraft suspension pylon.
In the event that one of the three suspension rods breaks, the two remaining rods must withstand the entire load which was previously spread over the three rods. This presents the danger of consecutive breaking of the two remaining rods thereby causing the total failure of the engine support system. Even in the event that the two remaining rods fail to break, the rotational torque generated by the engine and applied to the anti-torque bars may become excessive, thereby causing damage to the engine.
In order to prevent such a catastrophic failure of the engine support system, safety systems have been proposed. One such solution consists in doubling the rear suspension rods in the three axes. However, this solution to the problem has generated suspension systems with excess weight and complexity due to the necessity of forming the spare support elements of sufficient size and strength so as to enable it to withstand the maximum forces generated upon failure of the primary suspension system.
British Pat. No. 1,236,917 describes a turbojet engine suspension system in which an additional safety rod is incorporated into the normal three rod suspension system. However, no means are described for changing the position of the safety rod fro a normal, non-supporting position, to one in which it serves to support at least a partial engine load.
Other engine suspension systems are known in which an additional, safety rod normally performs no suspension function, however, should one of the normal support rods fracture, the safety rod then absorbs at least a part of the engine weight. However, these systems typically involve fixed clearances in the rod mounting such that these clearances are maintained during the normal suspension operation to prevent the rod from bearing any engine loads. Upon failure of one of the other suspension rods, the clearancese are taken up by engine movement such that the safety rod performs a support function.